RIYADH (AFP) — Saudi Arabia on Tuesday called on the United Arab Emirates (UAE) to withdraw its forces from Yemen and cease providing support to any groups in the country within 24 hours, backing a similar call from the Yemeni government in Aden.   

“The Kingdom stresses the importance of the sisterly state of the United Arab Emirates responding to the Republic of Yemen’s request for the withdrawal of its military forces from the Republic of Yemen within 24 hours, and for the cessation of any military or financial support to any party inside Yemen,” the foreign ministry said in a statement published online. 

Saudi Arabia declared a UAE-backed separatist advance in Yemen as a threat to Riyadh’s national security on Tuesday and called Abu Dhabi’s actions “highly dangerous,” as the conflict boiled over into an open dispute between the Gulf powers.

The strongly worded foreign ministry statement came after the Saudi-led coalition fighting in Yemen said it had struck a UAE weapons shipment destined for separatist forces.

In recent weeks, separatists backed by Abu Dhabi and seeking to revive the formerly independent state of South Yemen have made sweeping territorial gains after launching a lightning offensive in recent weeks.

Experts say their successes have embarrassed Saudi Arabia, a regional heavyweight and the main backer of the internationally recognized Yemeni government.

The Saudi ultimatum follows the leader of Yemen’s presidential council declaring a state of emergency and cancelling a security pact with the UAE on Tuesday after Abu Dhabi-backed separatists seized swathes of territory.territory.

“The Joint Defense Agreement with the United Arab Emirates is hereby cancelled,” a statement said, while a separate decree announced a 90-day state of emergency including a 72-hour air, sea and land blockade.

The announcements were made by Rashad al-Alimi, head of the Presidential Leadership Council.

The UAE-backed Southern Transitional Council (SCT) forces have swept through the south of Yemen this month, taking most of resource-rich Hadramawt province and swathes of neighboring Mahrah.

Alimi ordered the SCT to hand over the territory to Saudi-backed forces, calling the separatists’ advance an “unacceptable rebellion” in a televised address.

The confrontation risks tearing apart the already fractured Yemeni government, which has different factions backed by oil-rich Gulf powers Saudi Arabia and the UAE.

It also threatens slow-moving peace negotiations with the Iran-backed Houthi rebels, who ousted the government from the capital Sanaa in 2014, triggering a military intervention by the Saudi-led coalition.